Low-E Glass Secondary Glazing — Everything You Need to Know

What is Low-E Glass?

Low-E glass has a microscopic metallic coating applied to one surface. This coating reflects long-wave infrared radiation (heat) while transmitting short-wave solar radiation (light). The result is a glass that lets light through but significantly reduces heat loss through the window.

Performance

Standard 4mm toughened glass secondary glazing (face-fixed, 80mm cavity): reduces heat loss by approximately 50%, U-value around 2.0 W/m²K. Low-E toughened glass secondary glazing (face-fixed, 80mm cavity): reduces heat loss by up to 65%, U-value around 1.5 W/m²K. A meaningful improvement, particularly for properties with many windows.

When to Specify Low-E

Low-E glass is recommended when: thermal performance is a priority; energy bills are a significant concern; the property is in an exposed location; or the primary window is particularly poor performing (very old single glazing).

Low-E vs Acoustic

Low-E glass provides better thermal performance. Acoustic laminate glass provides better noise reduction. For most urban properties where both noise and thermal performance matter, acoustic laminate glass with Low-E coating combined is the premium specification.